JP4909653B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a deflection mirror (vibration mirror) that can be applied to an optical scanning device, an optical scanning display device, an in-vehicle laser radar device, and the like, an optical scanning device using the deflection mirror, and light thereof. The present invention relates to an image forming apparatus such as a digital copying machine, a printer, a plotter, a facsimile, and a digital copying machine using a scanning device.

  Conventionally, an optical scanning device that deflects a light beam by a deflecting means such as an optical deflector, forms an image of the deflected light beam as a fine spot light on a surface to be scanned, and scans the surface to be scanned at a constant speed in the main scanning direction. And is applied to latent image writing means of image forming apparatuses such as laser beam printers, laser beam plotters, facsimiles, and digital copying machines. This optical scanning device scans a surface to be scanned such as an image carrier by, for example, deflecting and reflecting laser light emitted from a laser light source with an optical deflector, and at the same time, responds to the laser light in accordance with an image signal. Thus, the image is written on the surface to be scanned by intensity modulation (for example, on and off).

  As the optical deflector, a rotating polygon mirror (polygon scanner) that rotates at a constant speed is widely used. However, the rotating polygon mirror requires a large apparatus, and also involves mechanical high-speed rotation. There are problems such as temperature rise, noise, and increased power consumption. On the other hand, a micromirror that performs sinusoidal vibration of a resonance structure using micromachine technology has been proposed. If this micromirror is used as a deflecting means of an optical scanning device, the device can be miniaturized and banding due to vibration, temperature rise, noise, power consumption, and the like can be greatly reduced.

  That is, by using a micro mirror that performs sine wave vibration as a substitute for a polygon mirror, noise and power consumption can be reduced, and an image forming apparatus suitable for an office environment or a global environment can be provided.

  However, if a micromirror that performs sinusoidal vibration is used as a deflecting means, the deflection angle changes sinusoidally, so that the fθ lens used in the current writing optical system is used as the scanning imaging optical system. The scanning speed becomes slow at the peripheral image height, and the scanning speed on the scanned surface is not constant. If the scanning speed is not uniform, there is a problem in that image distortion or the like occurs in the vicinity of the main scanning direction, causing deterioration in image quality.

With respect to this problem, in Patent Document 1, the following equation:
H = K × sin−1 (φ / 2φ ₀ ) (1)
However, the waist of the main scanning light beam is obtained by using a scanning imaging optical system having imaging characteristics (farcsin characteristics) as shown by H: image height, K: proportionality constant, φ: deflection angle, and φ ₀ : amplitude. It is described that the position is optically corrected to obtain an optical scanning device having a wide effective writing width and good constant scanning speed. As a result, the deviation between the image heights of the spot diameters of the main scanning light flux on the surface to be scanned becomes large, which eventually leads to deterioration of image quality.

  In an optical scanning device using a micromirror that performs sinusoidal vibration as a deflecting means, there is a trade-off relationship between the scanning constant velocity and the deviation in the spot diameter image height of the main scanning light beam on the scanned surface. An optical scanning device that forms a good and high-quality image could not be provided.

  In Patent Document 1, the sensitivity (scanning speed) of the peripheral image height with respect to the sensitivity (scanning speed) of the central image height with respect to the sensitivity of the imaging position, that is, the scanning speed with respect to the incident angle of the light beam to the deflecting means. There is a description of an embodiment in which a scanning imaging optical system with the same or smaller (velocity) is used to reduce the deviation between the image heights of the spot diameter of the main scanning light beam on the surface to be scanned. This is because a scanning imaging optical system in which linearity is almost zero at all image heights on the scanned surface or linearity at the peripheral image height is generated on the negative side, and the spot diameter image height of the main scanning light beam on the scanned surface is used. This means that the inter-deviation is reduced, but any of the embodiments of Patent Document 1 has the following problems and has not yet solved the above problem.

  In Example 1 in Patent Document 1, the deflection means determines the main scanning light beam width, whereby the spot diameter of the main scanning light beam on the surface to be scanned at the peripheral image height is larger than the central image height. However, by giving the scanning imaging optical system characteristics that degrade the linearity to the minus side, that is, by generating linearity further on the minus side than when the fθ lens is used as the deflecting means, the main scanning light beam The spot diameter is corrected. In the first embodiment, a good deviation of the spot diameter image height of the main scanning light beam is obtained, but since the linearity is generated further on the minus side than when the fθ lens is used as the deflecting means, the scanning is performed. The isovelocity is greatly deteriorated, and a high-quality image cannot be obtained.

  In Example 2 in Patent Document 1, in an optical scanning device in which the deflecting means determines the main scanning light beam width, an fθ lens is used for the scanning imaging optical system, and a micromirror that performs sinusoidal vibration as the deflecting means is used. The deflection angle is set smaller than the maximum amplitude. By reducing the deflection angle of the micromirror, the deflection speed is dominated by a linear change rather than a sinusoidal change, and a good scanning constant velocity and a good main scanning beam spot diameter deviation between image heights. However, since the deflection angle of the micromirror is reduced, the distance from the micromirror to the surface to be scanned must be increased in order to obtain the effective writing width required when forming an image, and optical scanning is performed. There is a problem that the size of the apparatus is increased, which limits the size of the apparatus.

  In Example 4 in Patent Document 1, an fθ lens is used in the scanning imaging optical system in the optical scanning device having the configuration as shown in FIG. 1 according to the present invention. In this case, as described above, the scanning speed is slow at the peripheral image height, and the scanning speed on the surface to be scanned is not constant. If the scanning speed is not uniform, there is a problem in that image distortion or the like occurs in the vicinity of the main scanning direction, causing deterioration in image quality.

In Patent Documents 2 and 3, in an optical scanning device using a micromirror that performs sinusoidal vibration as a deflecting unit, a scanning imaging optical system having imaging characteristics as described in the above equation (1) is used. Rather than performing optical correction of the waist position of the scanning light beam, the deflection angle of the micromirror is reduced with respect to the maximum amplitude. As described above, the deflection speed in this case is dominated by a linear change rather than a sinusoidal change, and a good scanning constant velocity and a good deviation in image height between main scanning beam spot diameters can be obtained. However, since the deflection angle of the micromirror is reduced, there is a problem that the optical scanning device is enlarged in order to obtain an effective writing width necessary for forming an image, and the device size is restricted.
JP 2005-215571 A JP 2002-258204 A JP 2002-82303 A

  As a function of the optical scanning device, when the light beam deflected and reflected by the optical deflector is scanned on the surface to be scanned, the scanning speed on the surface to be scanned and the spot diameter deviation of the main scanning light beam are both good. And having a predetermined effective writing width necessary for image formation is indispensable in an optical scanning apparatus and an image forming apparatus that can improve the image quality and reduce the size of the apparatus. is there. It is indispensable to have a similar function when using a deflection mirror utilizing the above resonance.

Conventionally, according to sine wave vibration,
H = K × sin−1 (φ / 2φ ₀ ) (1)
However, using a scanning imaging optical system having imaging characteristics represented by H: image height, K: proportionality constant, φ: deflection angle, and φ ₀ : amplitude, while having a predetermined effective writing width. The waist position of the main scanning light beam was optically corrected to obtain a good scanning constant velocity. However, when the scanning imaging optical system having the imaging characteristic of equation (1) is used, the spot diameter of the main scanning light beam is reduced. It is known from Patent Document 2 that a deviation between image heights is generated.

  Also, a conventional scanning imaging optical system having imaging performance such as an fθ lens that scans a light beam deflected and reflected by a deflection means such as a polygon mirror that rotates at a constant speed on a surface to be scanned at a constant speed. When used in a writing optical system using a deflection mirror that utilizes the above-described resonance that vibrates sinusoidally, it has a predetermined effective writing width and has an image height of the spot diameter of the main scanning light beam on the surface to be scanned. Although the deviation can be reduced, the linearity on the surface to be scanned is greatly negative and the scanning constant velocity is deteriorated.

  In addition, if the deflection angle of the deflecting mirror using the resonance that sine wave vibrates is reduced, it is possible to obtain good scanning constant velocity and good deviation between the image heights of the spot diameter of the main scanning light beam on the scanned surface. In order to have a predetermined effective writing width, the distance from the deflecting mirror to the surface to be scanned must be increased, resulting in an increase in the size of the apparatus.

  The present invention has been made in view of the above circumstances, and scans the light beam deflected and reflected by the optical deflector on the surface to be scanned at a substantially constant speed, and detects the spot diameter deviation of the main scanning light beam on the surface to be scanned. An object of the present invention is to provide an optical scanning device having a large deflector deflection angle for a predetermined effective writing width, and an image forming apparatus using the optical scanning device.

In order to achieve the above object, an optical scanning device of the present invention includes a light source, a light source driving unit that turns on the light source according to image information, a deflection unit that deflects and scans a light beam from the light source by sinusoidal vibration, An optical scanning apparatus having a scanning imaging optical system that guides a light beam from the deflection means onto the surface to be scanned, where the scanning imaging optical system has the following conditions, and <1> it is assumed that the deflection means moves at an angular velocity. The linearity in the effective writing width range becomes positive, and <2> the linearity in the effective writing width range becomes negative when the deflection angle φ by the deflecting means does not change at a constant angular velocity. , And the following conditional expression: −0.09 <Lin. × (φ _max / φ ₀ ) <0 (where Lin .: minimum value of linearity when the deflection angle oscillates sinusoidally, φ ₀ : amplitude angle (°) of sinusoidal oscillation of the deflection means, φ _max : The maximum rotation angle (°) of the deflecting means corresponding to the effective writing width is satisfied .

In the optical scanning apparatus of the present invention, the light source driving means may be characterized by having a function of individually setting lighting start timing for each pixel in one line.

In the image forming apparatus of the present invention, after the image carrier is charged by the charging unit, the image carrier is exposed to light by the optical writing unit to form a latent image, and the latent image is developed by the developing unit. In the image forming apparatus for forming the image by transferring the visible image on the image carrier onto the transfer material by the transfer unit after forming the visible image, the optical scanning device of the present invention is used as the optical writing unit. It is characterized by that.

In the image forming apparatus of the present invention may be characterized by having a plurality of light sources, a plurality of image bearing members.

According to the present invention, the light source, the light source driving means for turning on the light source according to the image information, the deflection means for deflecting and scanning the light beam from the light source by sinusoidal vibration, and the light beam from the deflection means on the surface to be scanned A scanning imaging optical system, and the scanning imaging optical system has the following conditions:
<1> When it is assumed that the deflecting means moves at a constant angular velocity, the linearity in the range of the effective writing width is positive.
<2> When the deflection angle by the deflecting means does not change at a constant angular velocity, the linearity in the range of the effective writing width becomes negative.
In other words, that is, the linearity is generated on the minus side of the linearity when using the scanning imaging optical system having the imaging characteristic of the function (1), and a good spot of the main scanning light beam An intermediate between the two to obtain a deviation in the radial image height and to obtain a good scanning constant velocity by correcting the linearity when using a scanning imaging optical system having an imaging performance such as an fθ lens. By having the scanning imaging optical system having the above characteristics, it is possible to achieve good scanning without narrowing the deflection angle of the deflecting mirror using the resonance that vibrates sinusoidally, that is, having a predetermined effective writing width. Scanning constant velocity on the surface and a deviation between the image heights of the spot diameter of the main scanning light beam on the surface to be scanned can be obtained, thereby miniaturizing the apparatus, banding due to vibration, temperature rise, noise, Power consumption Etc. greatly reduces, adapted to the office environment and the global environment, at low cost, it is possible to provide an optical scanning device for forming a high-quality image. At this time, the linearity remains on the minus side, but the scanning constant velocity can be further improved by correcting the main scanning light beam waist position by the light source driving means described later.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

Hereinafter, the configuration, operation, and action of an optical scanning device according to the present invention and an image forming apparatus using the optical scanning device will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing an embodiment of an optical scanning device according to the present invention. FIG. 1A is an optical system layout diagram of a cross section (main scanning cross section) along the main scanning direction of the optical scanning device. FIG. 5B is an optical system layout diagram of a section (sub-scan section) along the sub-scanning direction of the optical scanning device. 1A and 1B, reference numeral 1 denotes a semiconductor laser (LD) which is a light source, 2 denotes a collimating lens that makes a divergent light beam from the semiconductor laser a substantially parallel light beam, and 3 denotes an aperture for limiting the light beam diameter. Is a cylindrical lens having refractive power only in the sub-scanning direction, 5 is an incident mirror, 6 is a deflecting means for deflecting a light beam from a semiconductor laser, 7 is a scanning imaging lens of a scanning imaging optical system, and 8 is a surface to be scanned. is there.

  In the optical scanning device having the configuration shown in FIG. 1, a divergent light beam emitted from a semiconductor laser 1 as a light source is made into a substantially parallel light beam by a collimating lens 2 and is narrowed by the aperture 3 and then long in the main scanning direction. It passes through a cylindrical lens 4 for forming a line image. The light beam that has passed through the cylindrical lens 4 is reflected by the incident mirror 5 as shown in FIG. 1B, and is incident on the deflecting means 6 with an incident angle in the sub-scan section. The deflecting means 6 is used as a deflector to deflect and reflect the light beam. The light beam deflected by the deflecting means 6 passes through the scanning imaging lens 7 and forms an image on the scanned surface 8.

  Here, when it is assumed that the deflecting means is a polygon mirror, the scanning imaging lens 7 has a positive linearity in the effective writing width range, and when the deflecting means is a sinusoidal vibrating mirror, the effective writing width range. It has the characteristic that the linearity at is negative. In other words, the scanning imaging lens 7 balances the above-described trade-off relationship between the linearity on the surface to be scanned and the deviation in the spot diameter image height of the main scanning light beam so that both values are good. An optical scanning device that has excellent imaging characteristics, and thus has good linearity on the surface to be scanned and deviation between the spot diameter and image height of the main scanning beam without narrowing the deflection angle with respect to the maximum rotation angle of the deflecting means. Have gained.

  The linearity at this time is a value on the negative side of the linearity of the scanning imaging lens having the farcsin characteristic in order to improve the deviation between the spot diameter image heights of the main scanning light beam on the scanned surface, and The value is on the plus side of the linearity of the scanning imaging lens having the fθ characteristic for good linearity characteristics.

Further, the scanning imaging lens 7 has the following conditional expression −0.09 <Lin. × (φ _max / φ ₀ ) <0 (2)
However, Lin. : Linearity at each image height φ ₀ : Amplitude angle of sinusoidal vibration of deflection means (°)
φ _max : Maximum rotation angle (°) of the deflection means corresponding to the effective writing width
When the above condition is satisfied, a wider effective writing width, a better uniform velocity characteristic on the scanned surface, or an image height deviation of the spot diameter of the main scanning light beam on a smaller scanned surface is obtained. An optical scanning device can be obtained.

The design data of the embodiment of the present invention is shown below. Since this embodiment is not largely different from the optical scanning apparatus having the configuration shown in FIG. 1, it will be described with reference to FIG. The sine wave oscillating mirror which is the deflection means 6 is
φ ₀ : ± 25 °
φ _max : ± 15 °
Therefore, φ _max / φ ₀ = 0.600
It has the vibration characteristics.

  At this time, the light beam incident on the sine wave oscillating mirror as the deflecting means 6 is condensed and incident in the sub-scanning direction at one point on the sine wave oscillating mirror as the deflecting means 6.

  The lens surface on the light beam incident side of the scanning imaging lens 7 is denoted by 7a, and the lens surface on the light beam emission side of the scanning imaging lens 7 is denoted by 7b. The distance from the sinusoidal vibrating mirror as the deflecting means 6 to the lens surface 7a on the light beam incident side of the scanning imaging lens 7 is 54.14 mm, and from the lens surface 7b on the light beam emission side of the scanning imaging lens 7 to the scanned surface 8. The distance is 206 mm.

  Also, Rm is the paraxial radius of curvature in the main scanning direction, Rs is the paraxial radius of curvature in the sub-scanning direction, D is the thickness of the scanning imaging lens, and N is the refractive index at the working wavelength of 780 nm. The data is as shown in Table 1 below.

The surface shapes of the surfaces 7a and 7b of the scanning imaging lens 7 constituting the scanning imaging optical system can be expressed by the following equation (3).
X (Y, Z) = (1 / Rm) · Y ² / {1 + √ (1− (1 + a ₀ ) · (1 / Rm) ² · Y ² )} + a ₄ · Y ⁴ + a ⁶ · Y ⁶ + · .. + Cs (Y) .Z ² / {1 + √ (1−Cs (Y) ² .Z ² )} (3)
Here, Cs (Y) = 1 / Rs + b ₂ · Y ₂ + b ₄ · Y ₄ +...

Moreover, each coefficient in the said (3) formula in each surface is as follows.
(7a surface)
a ₀ = 1.34E + 01
a ₄ = −9.45E-07
a ₆ = 5.81E-10
a ₈ = −1.25E−13
a ₁₀ = 1.32E-17
b ₂ = -1.87E-05
b ₄ = 4.91E-09
b ₆ = −5.64E−13
However, E + 01 = × 10 ⁰¹ , E-07 = × 10 ^-07
This also has the same meaning in the following.
(7b surface)
a ₀ = −5.74E-01
a ₄ = −7.66E-07
a ₆ = 1.74E-10
a ₈ = 2.95E-14
a ₁₀ = 1.01E-18
b ₂ = −1.08E−05
b ₄ = -3.11E-09
b ₆ = 8.10E-13

  2 shows the linearity at the time of constant speed deflection with respect to the image height, FIG. 3 shows the linearity with respect to the image height in this embodiment, and FIG. 4 shows the main scanning light flux with respect to the image height in this embodiment. The spot diameter is shown.

Here, the linearity at the time of constant velocity deflection indicates the linearity when it is assumed that the deflecting means moves at a constant angular velocity, and is expressed by the following equation.
Lin. (Θ) = {[H (θ + Δθ) −H (θ)] / Δθ− [H (0 + Δθ) −H (0)] / Δθ} · 100 (%)
Lin. (Θ): Linearity at angle of view θ H (θ): Image height at angle of view θ Δθ: Fine angle

As shown in FIGS. 2 and 3, the scanning imaging lens 7 of this embodiment has a positive linearity in the range of the effective writing width when it is assumed that <1> the deflecting means moves at an equiangular velocity. <2> When the deflection angle by the deflecting means does not change at a constant angular velocity, the linearity in the range of the effective writing width becomes negative. In the optical scanning device of this embodiment, the linearity is -11.57% at the minimum.
Lin. × (φ _max / φ ₀ ) = − 0.069
And the following conditional expression:
-0.09 <Lin. × (φ _max / φ ₀ ) <0 (2)
Is satisfied.

  In this embodiment, a sinusoidal vibrating mirror is used as the deflecting means 6 and the scanning imaging lens 7 satisfying the above conditions is provided, so that the maximum rotation angle of the deflecting means corresponding to the effective writing width is large (± 15). °), the linearity is good (−11.57%), and the deviation between the image heights of the spot diameter of the main scanning light beam is good (10.50%) as shown in FIG.

As described above, according to the present embodiment, the light source, the light source driving unit that turns on the light source according to the image information, the deflection unit that deflects and scans the light beam from the light source by sinusoidal vibration, and the deflection unit A scanning imaging optical system that guides the light beam onto the surface to be scanned.
<1> When it is assumed that the deflecting means moves at a constant angular velocity, the linearity in the range of the effective writing width is positive.
<2> When the deflection angle by the deflecting means does not change at a constant angular velocity, the linearity in the range of the effective writing width becomes negative.
In other words, that is, the linearity is generated on the minus side of the linearity when using the scanning imaging optical system having the imaging characteristic of the function (1), and a good spot of the main scanning light beam An intermediate between the two to obtain a deviation in the radial image height and to obtain a good scanning constant velocity by correcting the linearity when using a scanning imaging optical system having an imaging performance such as an fθ lens. By having the scanning imaging optical system having the above characteristics, it is possible to achieve good scanning without narrowing the deflection angle of the deflecting mirror using the resonance that vibrates sinusoidally, that is, having a predetermined effective writing width. Scanning constant velocity on the surface and a deviation between the image heights of the spot diameter of the main scanning light beam on the surface to be scanned can be obtained, thereby miniaturizing the apparatus, banding due to vibration, temperature rise, noise, Power consumption Etc. greatly reduces, adapted to the office environment and the global environment, at low cost, it is possible to provide an optical scanning device for forming a high-quality image. At this time, the linearity remains on the minus side, but the scanning constant velocity can be further improved by correcting the main scanning light beam waist position by the light source driving means described later.

Further, according to this embodiment, the following conditional expression (2),
-0.09 <Lin. × (φ _max / φ ₀ ) <0 (2)
However, Lin. : Linearity at each image height, φ ₀ : Amplitude angle of sinusoidal vibration of deflection means (°), φ _max : Maximum rotation angle of deflection means corresponding to effective writing width (°)
Is less than the lower limit when the deflection angle of the deflection means with respect to the maximum rotation angle of the deflection means remains unchanged and the linearity that is a negative value deteriorates, or when the linearity remains unchanged and the deflection means with respect to the maximum rotation angle of the deflection means There is a case where the deflection angle becomes large. In the former case, an optical scanning device with a deteriorated linearity and good scanning constant speed cannot be obtained. In the latter case, when the deflection angle of the deflection unit with respect to the maximum rotation angle of the deflection unit increases, the change in scanning speed is a sine wave. The vibrational change becomes dominant and the linearity is deteriorated. However, since the linearity is not changed, the spot diameter deviation of the main scanning light beam is deteriorated with the optical correction to keep the linearity constant. Therefore, when the lower limit of the conditional expression is not reached, an optical scanning device in which both the linearity on the surface to be scanned and the deviation between the image heights of the spot diameters of the main scanning light beam cannot be obtained. The upper limit is exceeded when the deflection angle of the deflection unit with respect to the maximum rotation angle of the deflection unit is unchanged and the linearity is small, or when the linearity is unchanged and the deflection angle of the deflection unit with respect to the maximum rotation angle of the deflection unit is small. There are cases. In the former case, if optical correction is performed to reduce the linearity, as described above, the deviation in the spot diameter image height of the main scanning light beam on the surface to be scanned deteriorates. In the latter case, the maximum rotation of the deflecting means Increasing the angle is limited by the upper limit of the manufacturing conditions of the sine wave oscillating mirror, which is a deflecting unit, and if the deflection angle of the deflecting unit is decreased, the deflecting unit can secure an effective writing width necessary for forming an image. The distance from the scanning surface to the surface to be scanned must be increased, and the optical scanning device becomes larger. Therefore, when the upper limit of the conditional expression is exceeded, an optical scanning device in which both the deviation between the image heights of the spot diameter of the main scanning light beam on the surface to be scanned and the effective writing width are good cannot be obtained.
For the above reasons, in the optical scanning device of this embodiment, in the optical scanning device satisfying the conditional expression (2), a wider effective writing width, or a better linearity on the scanned surface, or A better deviation between the image heights of the spot diameters of the main scanning light beam on the surface to be scanned can be obtained. This reduces the size of the device, significantly reduces banding due to vibration, temperature rise, noise, power consumption, etc., and is suitable for office and global environments. Can be provided.

[Lower limit in conditional expression (2)]
Since the present embodiment is not significantly different from the configuration of the optical scanning device according to the first embodiment, the description will be continued with reference to FIG. Here, the difference from the first embodiment is that the amplitude angle φ ₀ of the sine wave oscillating mirror as the deflecting means 6 is
φ ₀ : ± 24 °
This is the point.

Further, the maximum rotation angle φ _max of the sine wave vibrating mirror corresponding to the effective writing width in the present embodiment is the same as in the first embodiment.
φ _max : ± 15 °
As a result,
φ _max / φ ₀ = 0.625
It has become. Compared with the first embodiment, the ratio of the maximum rotation angle corresponding to the effective writing width with respect to the amplitude angle of the sine wave oscillating mirror is larger. The change in the deflection angular velocity of the wave oscillating mirror deviates from the linear behavior and becomes a more sinusoidal behavior, and the degree of slowing down of the scanning speed at the peripheral image height increases, so that the linearity is more negative (−13.705%). ).

  Since the lens data is the same as that in the first embodiment, and the maximum rotation angle of the sine wave vibrating mirror corresponding to the effective writing width is also the same as that in the first embodiment, the spot diameter image of the main scanning light beam on the surface to be scanned is used. The height difference is equal to Example 1 (10.5%).

At this time,
Lin. × (φ _max / φ ₀ ) = − 0.086
This value is −0.09 <Lin. In conditional expression (2). × (φ _max / φ ₀ ) <0
It is a value near the lower limit of. If linearity is generated on the minus side as compared with the present embodiment, good scanning constant velocity cannot be obtained. For example, even if main scanning beam dot position correction by the light source driving means described later is used in combination, the correction amount has a limit as described above, and in any case, good scanning constant velocity can be obtained. Therefore, the image quality deteriorates. In addition, when the ratio of the maximum rotation angle corresponding to the effective writing width is increased with respect to the amplitude angle of the sine wave oscillating mirror, the change in the deflection angular velocity of the sine wave oscillating mirror becomes a sine wave behavior. The scanning speed at the peripheral image height becomes slower, and good scanning isokineticity cannot be obtained, and the image quality deteriorates. For the above reason, the lower limit value in the conditional expression (2) is set.

[Upper limit in conditional expression (2)]
Lin. × (φ _max / φ ₀ ) <0
In this case, the spot diameter deviation of the main scanning light beam is smaller than when the linearity is corrected to 0 with the farcsin lens having the imaging characteristic of the above formula (1), and an optical scanning device using the farcsin lens is provided. The upper limit value in the conditional expression (2) is set based on the fact that an image with better quality than the image to be formed is obtained.

Considering the specifications of the sine wave vibrating mirror as the deflecting means 6, the maximum rotation angle corresponding to the effective writing width, and the spot diameter deviation of the main scanning light beam that can guarantee the image quality, more preferably,
-0.09 <Lin. × (φ _max / φ ₀ ) <− 0.03 (4)
An optical scanning device having a scanning imaging system that satisfies the following conditional expression is preferable.

[Upper limit in conditional expression (4)]
Since the present embodiment is not significantly different from the configuration of the optical scanning device according to the first embodiment, the description will be continued with reference to FIG. Here, the difference from the first embodiment is that the amplitude angle φ ₀ of the sine wave oscillating mirror as the deflecting means 6 is
φ ₀ : ± 28 °
This is the point.

Further, the maximum rotation angle φ _max of the sine wave vibrating mirror corresponding to the effective writing width in the present embodiment is the same as in the first embodiment.
φ _max : ± 15 °
As a result,
φ _max / φ ₀ = 0.536
It has become. Compared to the first embodiment, the ratio of the maximum rotation angle corresponding to the effective writing width with respect to the amplitude angle of the sine wave oscillating mirror is smaller. The change in the deflection angular velocity of the wave oscillating mirror becomes a linear behavior, and the degree of slowing down of the scanning speed at the peripheral image height is reduced. Therefore, the negative linearity is corrected to the plus side, and the scanning constant velocity is improved. Head to (-6.676%).

  Since the lens data is the same as that in the first embodiment, and the maximum rotation angle of the sine wave vibrating mirror corresponding to the effective writing width is also the same as that in the first embodiment, the spot diameter image of the main scanning light beam on the surface to be scanned is used. The height difference is equal to Example 1 (10.5%).

At this time,
Lin. × (φ _max / φ ₀ ) = − 0.036
This value is −0.09 <Lin. In conditional expression (4). × (φ _max / φ ₀ ) <− 0.03
It is a value near the upper limit value. When the linearity, which is a negative value compared to the present embodiment, is corrected to the plus side and an attempt is made to obtain good scanning constant velocity, the deviation between the spot diameter image heights of the main scanning light flux increases by the amount for correcting the linearity, and the image It leads to quality degradation. Further, the current amplitude angle of the sine wave oscillating mirror is limited in the vicinity of the amplitude angle in this embodiment, and the maximum rotation angle corresponding to the effective writing width with respect to the amplitude angle of the sine wave oscillating mirror than in this embodiment. In order to reduce the ratio, the maximum rotation angle corresponding to the effective writing width must be reduced. At this time, in order to have a predetermined effective writing width, the distance from the deflection mirror to the surface to be scanned must be increased. There is a problem that the apparatus must be enlarged. For the above reason, the upper limit value in the conditional expression (4) is set.

[Main scanning beam dot position correction by light source driving means]
Since the present embodiment is the same as the configuration of the optical scanning device according to the first embodiment, the description will be continued with reference to FIG. Here, the difference from the first embodiment is that the light source driving means (not shown) for controlling the lighting of the light source 1 has a function of individually setting the lighting start timing for each pixel in one line. . Hereinafter, the configuration of the present embodiment will be described with reference to the model diagram shown in FIG.

  As shown in FIG. 3, in this embodiment, the linearity decreases as the peripheral image height is reached. Therefore, when the frequency of the image signal and the lighting start timing of each pixel are constant within one line, as shown in FIG. 5A, the dot interval becomes narrower toward the periphery, and a magnification error occurs on the image. To do. Therefore, by individually setting the lighting start timing for each pixel in one line by the light source driving means, the width of the exposure distribution in the main scanning direction becomes smaller toward the periphery as shown in FIG. 5B. However, the interval of each pixel in the main scanning direction of the exposure distribution can be made uniform. Although the integrated light quantity of each pixel differs as described above, if the light source driving means is provided with means for individually setting the lighting time for each pixel in one line, the integrated light quantity of the exposure distribution is made uniform for each pixel. can do.

  By making the interval and the integrated light quantity of each pixel in the main scanning direction of the exposure distribution uniform for each pixel, the spot position of the main scanning light beam on the surface to be scanned is uniformly scanned. In other words, by canceling out the magnification error on the image caused by the optical performance by electrical correction, the difference between the spot diameter image height deviation of the main scanning light beam on the scanned surface and the scanning isokinetic property is achieved. It is possible to obtain better scanning isokineticity without overcoming the trade-off relationship and degrading the deviation between the main scanning beam spot diameter and the image height. Thereby, it is possible to obtain an optical scanning device in which the maximum rotation angle for the effective writing width of the deflecting means 6, the deviation in the spot diameter image height of the main scanning light beam on the surface to be scanned, and the scanning constant velocity are good. .

  As described above, according to the present embodiment, in addition to the configuration of the first embodiment, the light source driving means has a function of individually setting the lighting start timing for each pixel in one line. In addition to the effect of item 1 or 2, an optical scanning device capable of correcting the dot position of the main scanning light beam on the surface to be scanned and obtaining better scanning isokineticity and forming a higher quality image Can be provided.

  However, the dot position correction amount of the main scanning light beam by the light source driving means needs to be suppressed to a certain extent. When the scanning lens is molded in an ideal state and assembled to the optical scanning device, etc., in an ideal state, the linearity that is greatly generated on the minus side when the fθ lens is used is corrected by the light source driving means. However, in order to process a scanning lens, an optical scanning device, and the like in an ideal state, productivity must be reduced, and mass production cannot be performed, which results in high costs. Considering the efficient production of scanning lenses, optical scanning devices, etc. due to low cost, for example, scanning lens shape errors that occur during molding of scanning lenses and positioning errors that occur when mounting scanning lenses are avoided. Absent. When assembling the scanning lens into the optical scanning device, for example, if the scanning lens is shifted and assembled to the image height plus side, if the dot position correction amount of the main scanning beam by the light source driving means is large, the plus side peripheral image height In this case, the correction amount is extremely large, the dot position is corrected more than necessary, and the scanning speed is increased. In the peripheral image height on the minus side, the correction amount is extremely small, and the original scanning speed is not reached. As a result, good scanning isokineticity cannot be obtained and image quality is impaired. For the above reason, the waist position correction amount of the main scanning light beam by the light source driving means must be suppressed to a certain small value.

  The embodiments of the optical scanning device according to the present invention have been described above. In each of the above embodiments, a sine wave oscillating mirror is used as the deflecting means 6, but in addition to this, the deflection may be made by utilizing diffraction by a surface acoustic wave, or the deforming mirror is moved at a constant angular velocity. Thus, the deflection angle may not be changed at a constant angular velocity. In order to further increase the effective writing width, a plurality of scanning imaging optical systems may be arranged in the main scanning direction. Further, in the configuration example of FIG. 1, the light source 1 is a single semiconductor laser, but a multi-beam configuration using a plurality of semiconductor lasers, a semiconductor laser array having a plurality of light emitting points, and the like may be similarly implemented. It is possible and falls within the scope of the present invention. In the present embodiment, the deflecting means 6 may be configured by combining a sine wave oscillating mirror (deflection mirror) and a plurality of fixed mirrors so that a plurality of the reflecting means 6 is reflected at least once.

  Next, embodiments of the image forming apparatus according to the present invention will be described. FIG. 6 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. In FIG. 6, reference numeral 10 denotes a photoconductor on a drum which is an image carrier, 11 denotes a charging means for charging the photoconductor 10, and 12 denotes a latent image by exposing the charged photoconductor 10 with a light beam according to image information. 13 is a developing means for developing a latent image formed on the photoconductor 10 with, for example, toner to make a visible image, and 14 is a visible image (toner image) on the photoconductor 10. Transfer means for transferring to a transfer material 17 such as recording paper, 15 is a fixing means for fixing the visible image (toner image) transferred to the transfer material 17, and 16 is a cleaning means for cleaning the surface of the photoreceptor 10 after transfer. Yes, an image is formed on a transfer material and output by a process (electrophotographic process) of charging, exposure, development, transfer, fixing, and cleaning.

  In FIG. 6, a photoconductor 10 is obtained by forming a photoconductor layer (photosensitive layer) made of an inorganic material or an organic material on the surface of a drum-shaped conductive substrate, and the surface of the photoconductor becomes a scanned surface. . In addition to the drum shape, a belt shape may be used as the photoreceptor. The charging means 11 is a corona charger in the illustrated example, but various other devices such as a charging roller and a charging brush can be used. As the optical writing means 12, the optical scanning device having the configuration shown in FIG. 1 is used, and the details thereof are as described in the above-described embodiment. As the developing means 13, those having various configurations such as a developing device using a one-component developer consisting only of toner as a developer and a developing device using a two-component developer consisting of toner and carrier as a developer are used. be able to. The transfer means 14 is a transfer charger in the illustrated example, but various other devices such as a transfer roller, a transfer belt, and a transfer brush can be used. The fixing unit 15 fixes the image on the transfer material by heating and pressing, and includes a roller fixing unit using a heating roller and a pressure roller, a belt fixing unit using a belt and a heating unit, and the like. Various configurations can be used. As the cleaning means 16, various types of structures such as a blade type, a brush type, and a roller type can be used.

  FIG. 6 shows an example of a monochrome image forming apparatus, but the optical scanning device of the present invention can be used as an optical writing unit even when the configuration is a multicolor image forming apparatus of two or more colors or a full color image forming apparatus. Can be applied. In this embodiment, as shown in FIGS. 7 and 8, a plurality of light beams from a plurality of light sources corresponding to yellow, magenta, cyan, and black color materials are separated by a plurality of separation means 9Y, 9M, 9C, and 9K, respectively. A full-color image forming apparatus that guides light to a plurality of image carriers 10Y, 10M, 10C, and 10K corresponding thereto.

  FIG. 7 shows a plurality of image carriers (a plurality of light beams deflected and scanned by the deflecting means 6 when the multi-color light scanning device or the full color light scanning device of two or more colors is used in this embodiment). FIG. 2 is a schematic configuration diagram illustrating a state in which the photosensitive member is guided to 10Y, 10M, 10C, and 10K. A plurality of light beams from a plurality of light sources (not shown) are deflected by being incident on a deflection surface on one side of a single deflecting means 6 at different incident angles in the sub-scanning direction, and the plurality of light beams deflected and reflected are deflected. This is an image forming apparatus that forms a latent image by being separated by separation means 9Y, 9M, 9C, and 9K and scanned on the surfaces of a plurality of different image carriers 10Y, 10M, 10C, and 10K.

  Further, in the case of a configuration of a multi-color light scanning device or a full color light scanning device of two or more colors, a plurality of light beams from a plurality of light sources (not shown) are applied to both sides of a single deflecting unit 6 as shown in FIG. Are used to deflect at least two of the plurality of light beams incident on the deflection surface on one side of the deflecting means 6 at different incident angles in the sub-scanning direction. The image forming apparatus may be configured to form a latent image by separating and scanning each of the surfaces of a plurality of different image carriers 10Y, 10M, 10C, and 10K.

  As described above, according to this embodiment, a latent image is formed on the image carrier by using the optical scanning device described in any one of Embodiments 1 to 4 as the optical writing unit. When writing, while having a predetermined effective writing width, it is possible to achieve a constant speed on the surface to be scanned and a reduction in image height deviation of the spot diameter of the main scanning light beam on the surface to be scanned. It is possible to provide an image forming apparatus that forms a small image with low cost and good image quality.

  In addition, according to the present embodiment, the image forming apparatus includes a plurality of light sources and a plurality of image carriers, so that a full color tandem that forms a small, low-cost, low-color-shift image with good image quality. The image forming apparatus can be provided.

  As mentioned above, although each Example of this invention was described, it is not limited to said each Example, A various deformation | transformation is possible in the range which does not deviate from the summary.

  The present invention can be applied to an optical scanning device and an image forming apparatus in general.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows one Embodiment of the optical scanning device based on this invention, (a) is an optical system arrangement | positioning figure of the cross section (main scanning cross section) along the main scanning direction of an optical scanning device, (b) is an optical scanning device. It is an optical system arrangement | positioning figure of the cross section (subscanning cross section) along a subscanning direction. It is a figure which shows the linearity at the time of constant speed deflection with respect to image height in the optical scanning device of a present Example. It is a figure which shows the linearity with respect to the image height in the optical scanning device of a present Example. It is a figure which shows the spot diameter of the main scanning light beam with respect to the image height in the optical scanning device of a present Example. It is a figure for demonstrating the function which sets a lighting start timing separately for every pixel in 1 line. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. 1 is a schematic configuration diagram showing an embodiment of a full-color image forming apparatus having a one-side oblique incidence light scanning device according to the present invention. 1 is a schematic configuration diagram showing an embodiment of a full-color image forming apparatus having an opposed scanning oblique incidence light scanning device according to the present invention.

Explanation of symbols

1 Light source (semiconductor laser)
2 Collimating lens 3 Aperture 4 Cylindrical lens 5 Incident mirror 6 Deflection means (deflection mirror)
7 Scanning imaging lens 7a Beam entrance surface of scanning imaging lens (scanning imaging optical system) 7b Beam exit surface of scanning imaging lens (scanning imaging optical system) 8 Scanned surface 9Y Folding mirror for yellow 9M Folding for magenta Mirror 9C Folding mirror for cyan 9K Folding mirror for black 10Y Photoconductor for yellow (image carrier)
10M Magenta photoconductor (image carrier)
10C Cyan photoreceptor (image carrier)
10K black photoconductor (image carrier)
11 Charging means 12 Optical writing means (optical scanning device)
13 Developing means 14 Transfer means 15 Fixing means 16 Cleaning means

Claims (4)

A light source, light source driving means for turning on the light source in accordance with image information, deflection means for deflecting and scanning the light beam from the light source by sinusoidal vibration, and scanning connection for guiding the light beam from the deflection means onto the surface to be scanned. An optical scanning device having an image optical system,
The scanning imaging optical system has the following conditions:
<1> When it is assumed that the deflecting means moves at an equiangular velocity, in the range of the effective writing width, the linearity at the most peripheral image height is made larger than the linearity at the central image height;
<2> When the deflection angle by the deflecting means has a sine wave characteristic, the linearity at the most peripheral image height is made smaller than the linearity at the central image height in the effective writing width range;
Satisfied ,
The following conditional expression:
-0.09 <Lin. × (φ _max / φ ₀ ) <0
(However, Lin .: minimum value of linearity when the deflection angle oscillates sinusoidally,
φ ₀ : Amplitude angle of sinusoidal vibration of deflection means (°)
φ _max : Maximum rotation angle of deflection means (°) corresponding to effective writing width
An optical scanning device characterized by satisfying The optical scanning device according to claim 1 ,
The light source driving unit has a function of individually setting a lighting start timing for each pixel in one line. After the image carrier is charged by the charging unit, the image carrier is exposed to light by the optical writing unit to form a latent image, and the latent image is developed by the developing unit to be visualized. In an image forming apparatus that forms an image by transferring a visible image on an image carrier onto a transfer material by a transfer unit,
An image forming apparatus using the optical scanning device according to claim 1 or 2 as the optical writing unit. The image forming apparatus according to claim 3 .
An image forming apparatus comprising: a plurality of light sources; and a plurality of image carriers.

Images